In the early days of planet hunting -- which is to say, just a few years ago -- most of the discoveries were “hot Jupiters” -- giant planets orbiting quite close to their parent stars. Today, some discoveries also invoke comparisons to Jupiter, but in a quite different way. In these cases, the stars are about the same size as Jupiter -- and in one, the entire system resembles Jupiter and its four largest moons.

It’s known as KOI-961. It was discovered by Kepler -- a space telescope that’s watching 150,000 stars for evidence of planets. Kepler’s found close to 2,000 possible planetary systems, which astronomers are trying to confirm. They’ve done that with KOI-961.

The star itself is a red dwarf -- a cool ember of a star that’s only a fraction as massive as the Sun and only about 70 percent larger than Jupiter.

Kepler has detected slight dips in the star’s overall brightness -- the result of three different planets passing across its face. Calculations show that the most distant of the planets is only a little farther out than the most distant of Jupiter’s big moons, and only a bit bigger than Jupiter’s largest moon. The other two planets are slightly larger, but not by much. That makes KOI-961 the smallest planetary system discovered -- so far.

Jupiter itself is in great view this evening. It’s just to the lower left of the Moon, and looks like a brilliant star. The even brighter planet Venus stands above them.

Script by Damond Benningfield, Copyright 2012

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